CERAMICS INTERNATIONAL ELSEVIER Ceramics International 30(2004)213-217 www.elsevier.com/locate/ceramint R-curve behavior of laminated SiC/Bn ceramics Dongyun Li Guanjun Qiao, Zhihao Ji State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering Xian Jiaotong University, Xi an 710049, PR China Received 22 November 2002: received in revised form 7 March 2003: accepted 7 April 2003 Abstract Laminated Sic/Bn ceramics with a perfect layered structure was fabricated by tap-casting process and hot-pressing sintering. Damage resistance and r-curve be of laminated Sic/Bn ceramics were evaluated using the indentation-strength-in-bending technique, and compared with those of monolithic SiC ceramics. The results showed that the indentation strengths for monolithic ceramics decreased steeply with indentation load, while for laminated SiC/bn ceramics reduced slightly with indentation loac suggesting an exceptional damage resistance. Moreover, a rising R-curve behavior was demonstrated for laminated Sic/Bn cera- mics, a plateau R-curve behavior for monolithic Sic ceramics. The excellent damage resistance and pronounced R-curve behavior of laminated SiC/BN ceramics were attributed to crack defection, crack branching and crack delamination at the Sic/Bn weak C 2003 Elsevier Ltd and Techna S.r.L. All rights reserved Keywords: B Interface: C. Fracture: C. Mechanical properties: D. Sic 1. Introduction achieved with strengths of 729 MPa and fracture toughness of 20.5 MPa m2. For the latter, damage When ceramic materials are applied to structural capability and oxidation resistance were improved in components, the lack of damage-tolerance is one of the comparison with microcomposites with a carbon inter most crucial problems. Ceramic composites with phase. These properties make this system attractive for layered structure have been considered to offer one of applications the most important approaches to this problem, and a In this paper, laminated SiC/BN ceramics(hereafter number of studies have been conducted so far in several denoted by LSB)with a perfect layered structure were systems including alumina zirconia [1-4], alumina /alu- fabricated by tap-casting process and hot-pressing sin minium titanate [5], mullite/alumina [6], silicon carbide tering. Damage resistance and R-curve behavior of LSB [7-10] and silicon nitride [11-13]. These laminated cera- are evaluated using the indentation-strength-in-bending mics have been reported to exhibit increased apparent technique(ISB), and compared with those of monolithic fracture toughness and fracture energy as well as a non- SiC ceramics(hereafter MS), the difference between the catastrophic fracture behavior. However, little work has two being analyzed been performed on the flaw tolerance and fracture resistance behavior of the layered ceramics Silicon carbon (SiC) layered ceramics with weak 2. Experimental procedure boron nitride (BN) interphases have been previously manufactured in a conventional two-dimensional 2. materials layered structure [14, as well as in microcomposites [15]. For the former, impressive properties were The flow chart for the fabrication process of LSB is shown in Fig. 1. Briefly, submicrometer silicon carbide 4 Corresponding author. Tel: +86-29-266-7942: fax: +86-29-266 powders with sintering additives 6 wt. alumina and 4 wt% yttria and the organic additives were mixed and E-mailaddressdongyunli(@hotmail.com(d.Li) cast into the green tapes, then coated with BN-containing 0272-8842/03/$30.00@ 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/S0272-8842(03)00091-9R-curve behavior of laminated SiC/BN ceramics Dongyun Li*, Guanjun Qiao, Zhihao Jin State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, PR China Received 22 November 2002; received in revised form 7 March 2003; accepted 7 April 2003 Abstract Laminated SiC/BN ceramics with a perfect layered structure was fabricated by tap-casting process and hot-pressing sintering. Damage resistance and R-curve behavior of laminated SiC/BN ceramics were evaluated using the indentation-strength-in-bending technique, and compared with those of monolithic SiC ceramics. The results showed that the indentation strengths for monolithic SiC ceramics decreased steeply with indentation load, while for laminated SiC/BN ceramics reduced slightly with indentation load, suggesting an exceptional damage resistance. Moreover, a rising R-curve behavior was demonstrated for laminated SiC/BN cera￾mics, a plateau R-curve behavior for monolithic SiC ceramics. The excellent damage resistance and pronounced R-curve behavior of laminated SiC/BN ceramics were attributed to crack deflection, crack branching and crack delamination at the SiC/BN weak interfaces. # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. Keywords: B. Interface; C. Fracture; C. Mechanical properties; D. SiC 1. Introduction When ceramic materials are applied to structural components, the lack of damage-tolerance is one of the most crucial problems. Ceramic composites with a layered structure have been considered to offer one of the most important approaches to this problem, and a number of studies have been conducted so far in several systems including alumina/zirconia [1–4], alumina/alu￾minium titanate [5], mullite/alumina [6], silicon carbide [7–10] and silicon nitride [11–13]. These laminated cera￾mics have been reported to exhibit increased apparent fracture toughness and fracture energy as well as a non￾catastrophic fracture behavior. However, little work has been performed on the flaw tolerance and fracture resistance behavior of the layered ceramics. Silicon carbon (SiC) layered ceramics with weak boron nitride (BN) interphases have been previously manufactured in a conventional two-dimensional layered structure [14], as well as in microcomposites [15]. For the former, impressive properties were achieved with strengths of
729 MPa and fracture toughness of
20.5 MPa m1/2. For the latter, damage capability and oxidation resistance were improved in comparison with microcomposites with a carbon inter￾phase. These properties make this system attractive for applications. In this paper, laminated SiC/BN ceramics (hereafter denoted by LSB) with a perfect layered structure were fabricated by tap-casting process and hot-pressing sin￾tering. Damage resistance and R-curve behavior of LSB are evaluated using the indentation-strength-in-bending technique (ISB), and compared with those of monolithic SiC ceramics (hereafter MS), the difference between the two being analyzed. 2. Experimental procedure 2.1. Materials The flow chart for the fabrication process of LSB is shown in Fig. 1. Briefly, submicrometer silicon carbide powders with sintering additives 6 wt.% alumina and 4 wt.% yttria and the organic additives were mixed and cast into the green tapes, then coated with BN-containing 0272-8842/03/$30.00 # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/S0272-8842(03)00091-9 Ceramics International 30 (2004) 213–217 www.elsevier.com/locate/ceramint * Corresponding author. Tel.: +86-29-266-7942; fax: +86-29-266- 5443. E-mail address: dongyun_li@hotmail.com (D. Li)